1. Field of the Invention
This invention relates to a holding device of industrial robots, helper robots, home-use robots and other robots, or of conveyance equipment, automated devices, etc. in various manufacturing processes, that holds various types of workpieces, articles of daily use such as cups, or other objects.
2. Description of the Prior Art
Prior art industrial robot holding devices include holding devices such as that disclosed in the JP-A HEI 4-159092 and shown in FIG. 1 and FIG. 2. This device is equipped with holding claws 2 (2a to 2c) having detectors 8 and auxiliary claws 6 that hold an object 9 and are operated in sync via a piston 7 by air cylinders 5 (5a to 5c) mounted on a base 1 and by links 3 (3a to 3c) and a rotational disc 4. This kind of prior-art holding device is equipped with air cylinders or other drive devices for multiple holding claws, thus making the mechanism complex
In addition, holding devices that drive via a pulley by means of a rope are disclosed in JP-A SHO 52-91266 and JU-A SHO 61-64985, but these use only one pair of holding fixtures and their mechanism is complex because they use many pulleys, gears, etc.
The inventor has already proposed as a previous invention (JP-A HEI 11-188683) a holding device equipped with a mechanism that employs a single drive source, such as a motor etc., to drive the holding fixtures of the holding device and is simple in structure, lightweight and compact. In addition, this mechanism utilizes a single rope to transfer the driving force to the holding fixtures and give equal holding force to all of the multiple holding fixtures regardless of the shape of an object being held, thereby holding the object precisely and stably and preventing damage given to the held objects due to unequal holding forces.
In the previous invention, however, due to frictional force between the holding fixtures and the object when tension is applied to the drive rope, the holding operation will stop before a sufficiently stable holding condition can be achieved. When an external force is exerted in such an unstable holding condition or when the tension on the drive rope is increased for further increasing the holding force to achieve a more stable holding condition, slip will occur between the object and the holding fixtures, thus causing a temporary unstable holding condition to occur and resulting in the held object falling or other problems.
This invention has been proposed to solve the problems of the previous invention, and its purpose is to offer a holding device that utilizes rolling contact between the holding fixtures and the object being held to prevent slip from occurring between the holding fixtures and the held object and achieve a smooth transition to a stable holding condition.
The holding device of this invention comprises a support frame; multiple pairs of holding fixtures mounted on the support frame; a holding fixture pulley attached to one holding fixture of each one pair of holding fixtures; at least one frame pulley attached to the support frame; a drive rope bridging between the holding fixture pulley and the frame pulley and having one end pulled in one direction and the other end fixed to the support frame; and a drive source that pulls the drive rope; whereby when the drive rope is pulled by the drive source, holding fixtures constituting each one pair of holding fixtures are linked to move symmetrically to each other in a direction that holds an object to be held, each one pair of holding fixtures move independently of other pairs of holding fixtures, and the holding fixtures of each one pair of holding fixtures are movable toward and away from each other on a straight line or on two parallel straight lines on a plane of the support frame; wherein the multiple pairs of holding fixtures have contact parts that contact the object when the object is being held, and at least one of the contact parts is disposed so that it is rotatable about an axis parallel to a line normal to the plane of the support frame to maintain a rolling contact with the object when holding the object.
In a preferred aspect of the invention, the holding device further comprises a braking means that constrains or applies resistance to the rotation of the contact part.
As described above, at least one of the contact parts of the holding fixtures is disposed such that it can rotate to maintain rolling contact with the object to be held, whereby slip occurring between the object and the holding fixtures during the holding operation is reduced to achieve a transition to a stable holding condition.
Further, by equipping the holding fixture with a breaking means for braking the rotation of the contact part, stable constraining of the object to be held can be continued after complete holding of the object, thus making it possible to precisely control the holding operation according to the type or attributes of the object to be held.